1. Field of the Invention
The invention relates to a system for monitoring the performance of an electric power distribution system, and more particularly, to the generation and presentation of a composite power quality indicator generated from user weighted statistical contributions of various system parameters. The invention also relates to a method of generating and presenting a composite power quality indicator.
2. Background Information
Various instruments for monitoring the performance of electric power systems, including power quality, are known. A wide range of instrumentation measuring individual characteristics, such as RMS currents and voltages, peak currents and voltages, power factor, current and voltage sags and swells, harmonic distortion, flicker and the like, have long been available and are in wide use. Unfortunately, such individual instruments have required vigilant monitoring of a multitude of separate instrument indicators by an operator at an electric power facility with the inevitable result of undesirable electrical events often going unnoticed.
In response to this, power quality monitoring instruments that monitor multiple electrical characteristics have been devised. Some of these instruments attempt to provide an operator with an indication as to whether or not an overall power quality at a given time is normal for a given power system. In these instruments, an overall power quality value representative of what is normal for a given power system is arrived at through statistical analysis of summations of combinations of measurements of some electrical characteristics and quality values assigned to other electrical characteristics over time. This is first done over an initial period (typically a week) and then over a relatively longer period (typically a year). An example of such a power quality monitoring instrument is disclosed in U.S. Pat. No. 7,050,913, incorporated herein by reference.
Unfortunately, the use of a summation of measurements and assigned quality values, even when multiplied by weighting factors to control their relative importance, is susceptible to allowing an indication of a deleterious power quality event indicated by an anomaly in only one of the measurements or assigned values to be missed. Summation is typically more likely to result in a more noticeable indication to an operator of there being a problem when multiple ones of the measurements and/or assigned values simultaneously reflect the occurrence of an undesired power quality event. Also, employing observed electrical characteristics of a power system over time as a basis for determining whether or not a power quality event has occurred is susceptible to allowing one or more measurements and/or assigned values reflecting an undesirable condition to be accepted as normal over time.